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Thread: importance of case dimensions

  1. #1

    importance of case dimensions

    I am reloading .308 winchester. I have a pair of digital calipers for which i am scrutinizing size differentials in brass. I am using a set of lee deluxe dies and am only neck sizing at the moment. I am finding neck sizes are different after resizing. They are only fractions of an inch different, but different none the less.The length of the brass differs also. It is in safe reloading parameters,according to lee manual, but still fractions out. Will these size differences matter, or should i only use brass with the same neck and length size. Regards, Ed.

  2. #2
    Interesting that you are doing this - and finding the differences. It seems to me that the average reloader loading for field work might never consider such a thing apart from two considerations.

    Too much length in the case neck due to brass 'flowing' unchecked and not length reamed, might eventualy reach far forward enough to intrude with the bullet and create a powerful crimping situation inside the chamber - and increased pressures.

    By the same token, there is a potential problem if the neck wall thickness increases too much.
    The seating action of the bullet pushes the neck wall outwards and that too can create a situation where the bullet is literaly choked or crimped for its full necked length inside the chamber, thus creating another potentially dangerous situation.

    I once had a reamer made with which to equalise the inside if .243 case necks after the resising die had resized them INWARDS to uniform OUTSIDE dimensions, but this was made specifically for the pocket set of dies which were operated with a mallet.

    I believe that dimensions given in a reloading manual are largely made on the assumption that the average dimensions on rifles will meet those specifications. If you are concerned, and because you are investigating this you probably are, then it might be a good idea to check on the interior dimensions of your whole chamber in order to see what YOUR rifle tolerances are.

    There are a whole lot of shooters far better qualified within this forum who can tell you just how to set about that. My experiences and comments are simple working ones which inevitably crop up as cases begin to outlive their 'sell-by' date.
    Good luck. K.

  3. #3
    Ed
    Everything you measure relating to reloading varies. The challenge is determining what's significant and that depends a lot on what you want to do with your rifle when it's loaded. The following site has a whole series of interesting articles:
    http://riflemansjournal.blogspot.com...ring-case.html
    The Lee manual is also a must read.
    Some folk get obsessed and spend a lot of money on measurement to explore some of the issues in the following article:
    http://www.6mmbr.com/casenecktools.html
    My recommendation is read widely, but don't buy any tools/gadgets.
    Rgds JCS
    Last edited by jcampbellsmith; 13-08-2010 at 09:34. Reason: didn't make sense

  4. #4
    Quote Originally Posted by eddie View Post
    I am reloading .308 winchester. I have a pair of digital calipers for which i am scrutinizing size differentials in brass. I am using a set of lee deluxe dies and am only neck sizing at the moment. I am finding neck sizes are different after resizing. They are only fractions of an inch different, but different none the less.The length of the brass differs also. It is in safe reloading parameters,according to lee manual, but still fractions out. Will these size differences matter, or should i only use brass with the same neck and length size. Regards, Ed.
    All of the above posts are good advice. I'll add that you are working way too hard at this. Take a deep breath and think: All the brass is made on machinery, all will have a variance in dimension. The only ones you really need to pay attention to are the case length -which you should attend to at every reloading. Neck thickness is important if you switch to military cases or decide to shoot oversized bullets. I'm guessing that you aren't planning on applying these variables.

    I know that you are a novice so put the calipers away and read up on reloading. Or go for a walk. Nothing worse than a newbie reloader with some virgin brass and a set of calipers.... unless it's the same guy with his once-fired brass in hand and the same calipers!~Muir

    (Don't worry. We've all done it!)

  5. #5
    Right-on Muir - I had it in my cranium to say something similar regarding heading straight down the road with brass and calipers, but in the light of one or two chains getting recently yanked regarding advice and safety to new reloaders, it somehow took a back-step and I forgot.

    One thing I did mean to mention, though, Eddie, is IF you think that varying neck thicknesses are affecting your accuracy despite the cases - as you say - being well within safety dimensions, then perhaps crimping might even out the bullet exit pressure.

    I'd be tempted to say that whilst your concerns are admirable and definitely on the side of safety, your calipers might be better in the box for now with new brass being used - and don't let a niggling worry turn into a black monster to spoil your reloading life.
    A very real example of all possible avenues of insurance being used to coerce people and boost sales onto an overstocked loading bench. It looks to me that in Muir and others like him you will have plenty of first rate advice and support. Forget the exhortations of the sales-pitch guys.
    OH I once had 2 sets of measuring calipers - one in every hand ! I gave one away then decided to use the other only when a question arose - and the headache went away !
    Opinions often differ according to unknown circumstances.

  6. #6
    I have measured just about every part of cases even sectioning them to do some. For no other reason than i wanted to know. I have a whole cabinet of measuring tools and three Digital "verniers" a Dila vernier caliper and even oddities such as a tube mic which is handy for checking thickness of brass in the necks. Only one of the Digital calipers was brought for reloading. and that set has been used for only that. The rest were brought for work but as I have them i]they do get used on occasions to answer my own curiousosity .

  7. #7
    You are right to ask Eddie as with reloading a mistake could, potentially, be quite a disaster and it takes a while to get a feel for what is right or wrong. However, if all your cases are within the max dimensions given in reloading manuals then you will be safe enough. Lee make a nice device for trimming cases that is just a fixed length pilot with a cutting device at the top, I use it every time I reload a case and while often it doesn't shave any brass off sometimes it does and so my cases are always the same length. It is relatively inexpensive and they make a shell holder that fits into a cordless screwdriver to turn the case against the cutting head.

    I'm relatively new at reloading and so am prone to measuring things myself but I must confess that the one time I had a serious reloading problem I couldn't, no matter how hard I tried, measure any difference. Some of my cases would not chamber after been resized, while others would and it became clear to me that it was the shoulder - body junction that was the cause of the problem but try as I might I was never able to measure any difference in that area. The old trick of marking them with a black marker pen and then seeing where they were contacting the chamber was what gave the game away. :-)
    Last edited by caorach; 13-08-2010 at 17:36. Reason: spelling, it is "cutting" not "gutting" :-)

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